Systems and methods for continuous mode force testing

ABSTRACT

Described herein is a method and system for testing a force or strain sensor in a continuous fashion. The method employs a sensor, a test fixture, a load cell, a mechanical actuator and tester hardware and software to simultaneously record signal outputs from the sensor and load cell as functions of time. The method provides time synchronization events for recording data streams between, for example, a linear ramp of the force on, or displacement of, the sensor and for extracting performance characteristics from the data in post-test processing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication No. 62/854,422, filed on May 30, 2019, and entitled“CONTINUOUS MODE FORCE TESTING,” the disclosure of which is expresslyincorporated herein by reference in its entirety.

FIELD OF TECHNOLOGY

The present disclosure relates to the testing of force sensors andstrain gauges used for converting force or strain into an electricalsignal.

BACKGROUND

When testing sensors such as force sensors and strain gauges, it isoften required to evaluate sensor response over a range of input valuesin order to assess performance to specifications. Current techniques fortesting require a range of force or strain values to be applied and tostabilize each force or strain mechanically and wait for electricalsignal variations to stabilize prior to taking each measurement. Therepeated process of applying a force or strain, waiting for mechanicaland electrical stabilization, taking a measurement of both force orstrain and electrical signal, and applying an additional force or strainvalue is time consuming and costly.

Accordingly, there is a need in the pertinent art for a less timeconsuming, lower-cost, test method for force sensors and strain gauges.

SUMMARY

The present disclosure pertains to a method of testing force sensors andstrain gauges comprising the application of a mechanical force or strainand measurement of a sensor electrical output. Each force or strainsensor can include a flexure and one or more piezoresistive straingauges. In one implementation, a mechanical force is applied with alinear ramping of the applied force while simultaneously measuring theelectrical output of the force sensor and the amount of force applied.Synchronizing events are introduced in the test sequence to allow forpost-processing and analysis of the data taken through variousmeasurement channels. The method enables faster, lower-cost, and moreaccurate measurements of force sensors and strain gauges.

An example testing system is described herein. The system includes atest fixture configured to provide electrical connection to a force orstrain sensor, a mechanical actuator configured to apply force to theforce or strain sensor, a load cell configured to measure an amount ofthe force applied to the force or strain sensor and a controllerconfigured to operate the mechanical actuator and simultaneously recordrespective output signals from the force or strain sensor and the loadcell.

In some implementations, the step of simultaneously recording respectiveoutput signals from the force or strain sensor and the load celloptionally includes sampling the respective output signals in a burstmode, where the burst mode is defined by a sampling frequency and asampling period.

In some implementations, the respective output signal from the force orstrain sensor is sampled with a first sampling frequency and a firstsampling period. Additionally, the respective output signal from theload cell is optionally sampled with a second sampling frequency and asecond sampling period. Optionally, the first and second samplingfrequencies are the same or different.

Alternatively or additionally, the force or strain sensor includes oneor more piezoresistive, piezoelectric, or capacitive transducers.

Alternatively or additionally, the system further optionally includes arobotic arm, where the mechanical actuator is optionally controlled bythe robotic arm. For example, the robotic arm is operably connected toand controlled by the controller.

Alternatively or additionally, the respective output signals from theforce or strain sensor and the load cell is stored in memory of thecontroller.

Alternatively or additionally, the respective output signals from theforce or strain sensor and the load cell is recorded as a function oftime. In some implementations the controller is configured to operatethe mechanical actuator to change the amount of the force applied by themechanical actuator from a first force value to a second force value,where the first and second force values are different. Optionally, thecontroller is further configured to operate the mechanical actuator tohold the first force value constant while recording the respectiveoutput signals from the force or strain sensor and the load cell as afunction of time, subsequently ramp the first force value to the secondforce value while recording the respective output signals from the forceor strain sensor and the load cell as a function of time, and hold thesecond force value constant while recording the respective outputsignals from the force or strain sensor and the load cell as a functionof time. In some implementations, the controller is further configuredto operate the mechanical actuator to use a transition from the firstforce value to the ramped force and a transition from the ramped forceto the second force value as temporal data synchronization pointsbetween the respective output signals from the force or strain sensorand the load cell.

Alternatively or additionally, the system can optionally include aflexible substrate can be included, where the force or strain sensor issoldered to the flexible substrate, and the force is applied to theflexible substrate by the mechanical actuator to create displacement andstrain within the flexible substrate and strain within the force orstrain sensor. In some implementations, the respective output signal ofthe force or strain sensor is recorded by the controller throughelectrical routing within the flexible substrate.

In some implementations, the system optionally includes the force orstrain sensor.

An example method for testing a force or strain sensor is also describedherein. The example method includes providing a test fixture configuredto provide electrical connection to the force or strain sensor,connecting the force or strain sensor to the test fixture, and operatinga mechanical actuator to apply a force to the force or strain sensor.The example method also includes providing a load cell configured tomeasure an amount of the force applied to the force or strain sensor,and simultaneously recording respective output signals from the force orstrain sensor and the load cell.

Additionally, the step of simultaneously recording respective outputsignals from the force or strain sensor and the load cell includessampling the respective output signals in a burst mode, where the burstmode is defined by a sampling frequency and a sampling period.

In some implementations, the respective output signal from the force orstrain sensor is sampled with a first sampling frequency and a firstsampling period. Additionally, the respective output signal from theload cell is sampled with a second sampling frequency and a secondsampling period. Optionally, the first and second sampling frequenciesare the same or different.

Alternatively or additionally, the force or strain sensor detects strainthrough piezoresistive, piezoelectric, or capacitive transducers.

Alternatively or additionally, the mechanical actuator is optionallycontrolled by a robotic arm. For example, the robotic arm is operablyconnected to and controlled by a computing device.

Alternatively or additionally, the respective output signals from theforce or strain sensor and the load cell are optionally stored in memoryof a computing device.

Alternatively or additionally, the respective output signals from theforce or strain sensor and the load cell is optionally recorded as afunction of time.

Alternatively or additionally, the method further includes changing theamount of the force applied by the mechanical actuator from a firstforce value to a second force value, where the first and second forcevalues are different. In some implementations, the method furtherincludes holding the first force value constant while recording therespective output signals from the force or strain sensor and the loadcell as a function of time, subsequently ramping the first force valueto the second force value while recording the respective output signalsfrom the force or strain sensor and the load cell as a function of time,and subsequently holding the second force value constant while recordingthe respective output signals from the force or strain sensor and theload cell as a function of time. Optionally, the method further includesusing a transition from the first force value to the ramped force and atransition from the ramped force to the second force value as temporaldata synchronization points between the respective output signals fromthe force or strain sensor and the load cell.

Alternatively or additionally, the force or strain sensor is soldered toa flexible substrate, and the force is applied to the flexible substrateby the mechanical actuator to create displacement and strain within theflexible substrate and strain within the force or strain sensor.Additionally, the respective output signals of the force or strainsensor is recorded through electrical routing within the flexiblesubstrate.

Other systems, methods, features and/or advantages will be or may becomeapparent to one with skill in the art upon examination of the followingdrawings and detailed description. It is intended that all suchadditional systems, methods, features and/or advantages be includedwithin this description and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The components in the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding partsthroughout the several views. These and other features of will becomemore apparent in the detailed description in which reference is made tothe appended drawings wherein:

FIG. 1 is an isometric view of the top of an example force sensor.

FIG. 2 is a cross-sectional view of the force sensor shown in FIG. 1.

FIG. 3 shows a cross-sectional view of another example force sensorsoldered to a substrate where a force is applied to the top of the forcesensor.

FIG. 4 shows a cross-sectional view of another example force sensorsoldered to a substrate where a force is applied to the bottom of thesubstrate.

FIG. 5 shows a typical voltage output response for a force sensor withrespect to input force level.

FIG. 6 shows the force applied to a force sensor versus time as measuredby a load cell according to an implementation described herein.

FIG. 7 shows an example voltage output signal versus time for a forcesensor experiencing the force profile shown in FIG. 6.

FIGS. 8A-8C show an example of the relative timing among force eventsapplied to a force sensor (FIG. 8A) and the resulting load cell forceoutput (FIG. 8C) and force sensor voltage output (FIG. 8B).

FIG. 9 shows a resulting voltage output versus force output measurementbased on post processing of load cell voltage output and force sensorvoltage output and the synchronization of force events (A and A′/B andB′).

FIG. 10 shows a cross-sectional view of a system for testing a force orstrain sensor according to an implementation described herein.

FIG. 11 is a block diagram of an example computing device.

DETAILED DESCRIPTION

The present disclosure can be understood more readily by reference tothe following detailed description, examples, drawings, and theirprevious and following description. However, before the present devices,systems, and/or methods are disclosed and described, it is to beunderstood that this disclosure is not limited to the specific devices,systems, and/or methods disclosed unless otherwise specified, and, assuch, can, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting.

The following description is provided as an enabling teaching. To thisend, those skilled in the relevant art will recognize and appreciatethat many changes can be made, while still obtaining beneficial results.It will also be apparent that some of the desired benefits can beobtained by selecting some of the features without utilizing otherfeatures. Accordingly, those who work in the art will recognize thatmany modifications and adaptations may be possible and can even bedesirable in certain circumstances, and are contemplated by thisdisclosure. Thus, the following description is provided as illustrativeof the principles and not in limitation thereof.

As used throughout, the singular forms “a,” “an” and “the” includeplural referents unless the context clearly dictates otherwise. Thus,for example, reference to “a force sensor” can include two or more suchforce sensors unless the context indicates otherwise.

The term “comprising” and variations thereof as used herein is usedsynonymously with the term “including” and variations thereof and areopen, non-limiting terms.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another aspect includes from the one particular value and/orto the other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint.

As used herein, the terms “optional” or “optionally” mean that thesubsequently described event or circumstance may or may not occur, andthat the description includes instances where said event or circumstanceoccurs and instances where it does not.

Throughout the present disclosure, the terms “force sensor” and “strainsensor” may be used to describe the sensor being tested. The systems andmethods disclosed can be used to test force sensors or strain sensors.In some implementations, the force or strain sensor is amicroelectromechanical system (“MEMS”) sensor.

The present disclosure relates to systems and methods for testing aforce or strain sensor. In the examples below, the systems and methodsare described with regard to testing a force sensor. It should beunderstood that force sensor testing is provided only as an example.This disclosure contemplates that the systems and methods describedherein can be used to test a strain sensor (or strain gauge). Withreference to FIG. 1 and FIG. 2, in some implementations the force sensor10 includes a base 11 and electrical contacts 19. The electricalcontacts 19 can be solder bumps, pillars, or other conductive contacts.It should be understood that the electrical contacts 19 provide themeans for applying voltage to and/or recording voltage from the forcesensor 10. A contact surface 15 exists along the top surface of the base11 for receiving an applied force F and transmitting the force F to atleast one mechanical flexure 16.

Referring again to FIGS. 1 and 2, a force sensor can include one or morediffused, deposited, or implanted sensing elements 22 on the bottomsurface 18 of the base 11. The bottom surface 18 is opposite to thecontact surface 15. The one or more sensing elements 22 can optionallyinclude a piezoresistive transducer, although this disclosurecontemplates using other transducer types such as piezoelectrictransducers or capacitive transducers. It should be understood that thenumber and/or arrangement of the sensing elements 22 shown in FIGS. 1and 2 are provided only as examples. This disclosure contemplates that aforce sensor can include more, less, and/or different arrangements ofsensing elements than as shown in FIGS. 1 and 2. As strain is induced inthe at least one mechanical flexure 16 proportional to the force F, alocalized strain is produced on the sensing element(s) 22 such that thesensing element(s) 22 experience compression or tension, depending onits specific orientation. As the sensing element 22 compresses andtenses its resistivity changes. The change in resistivity isproportional to the force F applied to the contact surface 15. Todetermine the force F, the resistivity can be measured and the force canbe calculated using the proportional relationship between resistivityand force. The resistivity can be measured using circuits configured tomeasure resistivity, for example according to an implementationdescribed herein, a Wheatstone bridge circuit 23 containing the sensingelements 22 produces a differential voltage proportional to the appliedforce F on the contact surface 15.

It should be understood that the force sensor 10 shown in FIGS. 1 and 2is provided only as an example of a force sensor. This disclosurecontemplates testing force sensors other than those shown in FIGS. 1 and2. Example MEMS force sensors that can be tested using the systems andmethods of this disclosure are described in detail in U.S. Pat. No.9,487,388, issued Nov. 8, 2016 and titled “Ruggedized MEMS Force Die;”U.S. Pat. No. 9,493,342, issued Nov. 15, 2016 and titled “Wafer LevelMEMS Force Dies;” U.S. Pat. No. 9,902,611, issued Feb. 27, 2018 andtitled “Miniaturized and ruggedized wafer level mems force sensors;”U.S. Pat. No. 10,466,119, issued Nov. 5, 2019 and titled “Ruggedizedwafer level mems force sensor with a tolerance trench;” WO2018/148503,published Aug. 16, 2018 and titled “INTEGRATED DIGITAL FORCE SENSORS ANDRELATED METHODS OF MANUFACTURE,” and WO2018/148510, published Aug. 16,2018 and titled “INTEGRATED PIEZORESISTIVE AND PIEZOELECTRIC FUSIONFORCE SENSOR,” the disclosures of which are incorporated by reference intheir entireties.

FIGS. 3 and 4 illustrate a force sensor 30 according to anotherimplementation described herein. Optionally, the force sensor 30 issoldered to a substrate 31 through solder balls 32. Optionally, thesubstrate 31 can be a flexible substrate, and electrical routing can bepositioned within the flexible substrate. This disclosure contemplatesthat the force sensor 30 can be any force sensor, including the MEMSforce sensors described above. As shown in FIG. 3, the force sensor 30can be activated from the top surface with force F to measure the forceF and output an electrical signal proportional to the applied force. Inthis implementation, the substrate is optionally held fixed in placewith backing material or other support material.

Referring to FIG. 4, the force sensor 30 can optionally be activated byapplying a force F from the bottom surface of the substrate 31. Theforce F can induce a displacement and strain in the substrate 31 whichin turn can impart strain to the force sensor 30 through solder balls32. In this implementation, the substrate 31 optionally has someflexibility while the top surface of the sensor 30 is optionallyunconstrained by any hard surface. The force sensor 30 can undergostrain and can output an electrical signal proportional to the amount ofstrain it experiences due to force F.

FIG. 5 illustrates a graph depicting typical output voltage signalversus input force for a force sensor, e.g., a force sensor such as onedescribed above with regard to FIGS. 1-4. According to conventionalforce sensor testing, a force value is set and held constant whilemeasuring output of the force sensor. This process is repeated at aplurality of force level increments to establish the response curve(i.e., the dotted line in FIG. 5) of the sensor. At each applied forcevalue, the output of the force sensor is allowed to stabilize beforemoving to the next incremental force value. The response curverepresents the voltage output (y-axis) versus applied force (x-axis).This disclosure contemplates that the force response of a force orstrain sensor is monotonic, e.g., the voltage output never decreases asthe values of the applied force increase. The linear force responseshown in FIG. 5 is provided only as an example. It should be understoodthat the force response curve for a force or strain sensor may benon-linear. This conventional testing method is time consuming sincechanging the applied force induces electrical and mechanical noise whichrequires settling time or averaging to reduce noise and enablemeasurement accuracy.

FIG. 6 illustrates a graph of force applied to a force sensor as afunction of time according to an implementation described herein. InFIG. 6, the force applied (or voltage output) is measured by the loadcell. As described herein, a load cell is a transducer that convertsapplied force into a measurable output voltage. In other words, thevoltage output of a load cell is indicative of the force applied to theload cell. The applied force is held at a fixed value F1 up to time t1.At time t1, the force begins to ramp with time, corresponding to point Ain the graph. As discussed below, the force increases continuously fromF1 to F2 between point A (at time t1) to point B (at time t2). In FIG.6, the force ramps linearly (e.g., increases linearly) with time. Itshould be understood that the linearly increasing applied forcebeginning at time t1 is provided only as an example. This disclosurecontemplates that the increasing applied force beginning at time t1 maydo so in a non-linear fashion. Additionally, it should be understoodthat the rate of increase shown in FIG. 6 is provided only as an exampleand that other rates of increase are possible. The force is continuallyramped to point B in the graph, where it is held at a fixed value F2starting at time t2. In FIG. 6, F2 is greater than F1. It should beunderstood that the values of F1 and F2 and times t1 and t2, as well asthe relationships therebetween, are provided only as examples.Additionally, a ramped increasing force is used in FIG. 6 as an example.It should be understood that force can be decreased, for example,between F2 and F1 over time. The x-axis in FIG. 6 represents time, andthe y-axis represents the applied force. It should be understood thatthe y-axis in FIG. 6 represents the voltage output of a load cell, whichis indicative of the applied force.

FIG. 7 illustrates the corresponding voltage output for a linear forcesensor experiencing the force profile illustrated in FIG. 6. It shouldbe understood that the force response of a force or strain sensor is notrequired to be linear. The response of a force or strain sensor, whetherlinear or non-linear, is expected to be monotonic. The linear forceresponse shown in FIG. 7 is provided only as an example. In FIG. 7, thevoltage output is measured by the force sensor. In other words, x-axisin FIG. 7 represents time, and the y-axis in FIG. 7 represents thevoltage output of the force sensor. There is a constant voltage outputV1 while the applied force F1 is constant. When the applied force beginsto ramp linearly at point A in FIG. 6, there is a corresponding changein the voltage output starting at point A′ in FIG. 7. This occurs attime t1′ in FIG. 7. It should be understood that the rate of increaseshown in FIG. 7 is provided only as an example and that other rates ofincrease are possible. Further, a delay is present between the inputforce and the output voltage of the force sensor. For example, a delaycan be caused by delays in the signal path and/or differences in thesignal path lengths for load cell (FIG. 6) and force sensor (FIG. 7),respectively. Therefore, the time t1′ in FIG. 7 is different than thetime t1 in FIG. 6. Similarly, t2 in FIG. 6 is different than t2′ in FIG.7.

As the force is ramped linearly as shown in FIG. 6, the voltage outputof a force sensor responds proportionally as shown between points A′ andB′ in FIG. 7. With reference to FIG. 7, the voltage output of the sensorincreases until point B′ which corresponds to a constant force level F2being applied. This occurs at time t2′ in FIG. 7. After point B′, thevoltage output is constant at voltage V2 corresponding to constant forceF2. Again, a delay can be caused by delays in the signal path and/ordifferences in the signal path lengths for load cell (FIG. 6) and forcesensor (FIG. 7), respectively.

FIGS. 8A-8C show an example of relative timing among events andmeasurements according to an implementation described herein. FIG. 8Aindicates the timing of an applied force to a force sensor (e.g., theforce sensors of any one of FIGS. 1-4), illustrated as a linear ramp inforce from point A to point B. The applied force is ramped continuouslyover time between points A and B (e.g., in contrast to incrementally orwith discreate steps). As described above, the linearly increasingapplied force and force response in FIGS. 6 and 7 are provided only asexamples. As shown in FIG. 8A, the applied force is held constant attimes before point A and also held constant at times after point B.Between points A and B, the applied force increases continuously from F1to F2. FIG. 8B illustrates the timing of voltage measurements from theforce sensor (also referred to herein as “force sensor output”).According to the implementation illustrated in FIGS. 8A-8C, the systemis configured to sample using a “burst mode.” In “burst mode,” thesensor and load cell are sampled in “bursts” where each burst includesplurality of voltage measurements (e.g., from either the force sensor orthe load cell) acquired in each “burst period.” In FIGS. 8A-8C, thevertical arrows represent samples, and the spacing between the verticalarrows represents the sampling period. The sampling rate for both thesensor output (FIG. 8B) and load cell output (FIG. 8C) can be tuned toreduce the measurement noise of a single burst mode reading, forexample, by means of averaging the plurality of voltage measurementsacquired in a burst. Additionally, the burst period is not fixed, andcan be adjusted to account for motor speed (e.g., driver of themechanical actuator), sensor output sensitivity, and/or other parametersparticular to a given measurement implementation. As shown in FIGS.8A-8C, a plurality of burst measurements are acquired from each of theforce sensor and load cell prior to points A and A′, a plurality ofburst measurements are acquired from each of the force sensor and loadcell between points A/A′ and B/B′, and a plurality of burst measurementsare acquired from each of the force sensor and load cell after points Band B′. It should be understood that a plurality of burst measurementsare acquired from each of the force sensor and load cell while theapplied force increases continuously between points A/A′ and B/B′. Inother words, according to the implementation shown in FIGS. 8A-8C, theapplied force is not increased incrementally (e.g., step-wise) betweenpoints A/A′ and B/B′ with a pause for measurements at an incrementalstep. FIG. 8C illustrates the timing of measurements from a load cell(also referred to herein as “load cell output”), which quantifies theamount of force applied to the force sensor as a function of time. Theload cell is also measured in a burst mode with a force sample period,and a burst period indicated by the time between groups of smallvertical arrows. As discussed above, the sampling rate for the load celloutput (FIG. 8C) can be tuned to reduce the measurement noise of asingle burst mode reading, for example, by means of averaging theplurality of voltage measurements acquired in a burst. Additionally, theburst period is not fixed, and can be adjusted to account for motorspeed (e.g., driver of the mechanical actuator), load cell outputsensitivity, and/or other parameters particular to a given measurementimplementation. Different combinations of force sensor, load cell,sampling mode, and sampling period are possible, according toimplementations described herein. For example, the output data from theforce sensor may be sampled with a first sampling frequency/period, andthe output data from the load cell may be sampled with a second samplingfrequency/period. According to some implementations described herein,the load cell sample period and force sensor sample period can be thesame. According to other implementations, the load cell sample periodand force sensor sample period can be different. Alternatively oradditionally, the load cell sample frequency and force sensor samplefrequency can be the same or different.

The actual timing of signal events between load cell measurements andforce sensor measurements will not in general be synchronous, but willoccur with some relative delay between the different signal paths, whichis indicated as delta t relative signal delay below FIG. 8C. After theload cell and force sensor voltage output signals have been measured andrecorded through the sequence shown in FIGS. 6 and 7 (e.g., fixed 1stforce (F1) until time t1/t1′, followed by ramped force until timet2/t2′, followed by fixed 2nd force (F2)), the signal data can be postprocessed to map the events at the beginning and end of the force ramp.Points A/A′ and B/B′ serve as the temporal data synchronization points.For example, the onset of the load cell voltage output signal increase(e.g., at time t1 in FIG. 6) is mapped to the onset of the force sensorvoltage output signal increase (e.g., at time t1′ in FIG. 7), andsimilarly the load cell voltage output stabilization (e.g., at time t2in FIG. 6) is mapped to the force sensor voltage output stabilization(e.g., at time t2′ in FIG. 7), to obtain a function of force sensorvoltage output as a function of load cell voltage output. Themeasurement times for one signal path can be shifted or scaledappropriately such that the start and end times for the force rampcoincide between load cell voltage output and force sensor voltageoutput. In some implementations, the load cell and force sensor voltageare sampled at the same rate, such that after scaling times on onevariable to match the start and stop events, the intermediate points canalso be scaled by the same factor to match values one to one betweenload cell output and sensor voltage output.

The transition points (e.g., points A/A′ and B/B′ in FIGS. 6 and 7) canbe used as temporal synchronization points. It should be understood thatthe number and/or relationship between the synchronization points areprovided only as an example. For example, by synchronizing the time atwhich the load cell output begins to change, with the point at which theforce sensor output begins to change, the two graphs can besynchronized, accounting for any time delay between the output from theforce sensor and the output from the load cell. Accordingly, the forcesensor output voltage can be determined as a function of the load cellforce measurement. By scaling the measurement times of one signal path,either force sensor voltage output or load cell voltage output, andmapping the start and stop force ramp events, the force sensor voltageoutput can be determined as a function of the load cell forcemeasurement, providing the desired signal output versus applied forcemeasurement as shown in FIG. 9. This can be accomplished withoutrepeating a plurality of force level increments and measurements toestablish the force sensor's response curve according to conventionaltechniques as discussed above with regard to FIG. 5.

FIG. 10 illustrates a cross-sectional view of a system for testing aforce or strain sensor. In FIG. 10, the system includes a test fixture44, a mechanical actuator 45, and a load cell 46. The system alsoincludes a controller (e.g., computing device 1100 shown in FIG. 11)operably coupled to the mechanical actuator 45 and the load cell 46.Additionally, the controller is operably coupled to a force sensor 40via the test fixture 44. This disclosure contemplates that the forcesensor 40 can be any one of the force sensors as described above, oranother other type of force or strain sensor. The controller can becoupled to the mechanical actuator 45, load cell 46, and/or force sensor40 through one or more communication links. This disclosure contemplatesthe communication links are any suitable communication link. Forexample, a communication link may be implemented by any medium thatfacilitates data exchange including, but not limited to, wired, wirelessand optical links.

The test fixture 44 can be made (or coated with) of an insulatingmaterial and include one or more electrical connections 43. Optionally,as shown in FIG. 10, the electrical connections 43 are provided in arecess of the text fixture 44, where the recess is configured to fit theforce sensor 40. This disclosure contemplates that insulating materialsinclude, but are not limited to, polyether ether ketone (PEEK), ceramic,and polyimide. This disclosure also contemplates that the electricalconnections 43 can be made of a conductive material (e.g. metal). Theelectrical connections 43 can be provided to make contact with solderballs (or pillars, terminals, etc.) 42 of the force sensor 40. It shouldbe understood that the solder balls 42 provide the means for applyingvoltage to and/or recording response (e.g., voltage output) from theforce sensor 40. The number, size, shape and/or arrangement of theelectrical connections 43 can be chosen based on the design of the forcesensor 40. It should be understood that the number, size, shape and/orarrangement of the electrical connections 43 in FIG. 10 are providedonly as examples. The test fixture 44 therefore serves as anelectrically insulating mechanical fixture with conductive electricalconnections 43 for providing source voltage and/or measuring outputvoltage of the force sensor 40. The force sensor 40 can be operablycoupled to the controller (e.g., computing device 1100 shown in FIG. 11)via the electrical connections 43. Accordingly, the system is configuredto record the force sensor output voltage (e.g., as shown in FIGS. 7 and8B) via the electrical connections 43 while a force is applied to theforce sensor 40.

The system also includes the mechanical actuator 45. The mechanicalactuator 45 is configured to apply the force to the force sensor 40. Forexample, the mechanical actuator 45 can be a moveable rigid body. Themechanical actuator 43 can be made of a hard plastic (e.g., an acetalhomopolymer such as DELRIN), metal (e.g. aluminum, stainless steel,etc.), or an elastic material (e.g., silicone rubber). This disclosurecontemplates the mechanical actuator's size and/or shape are variable.For example, the mechanical actuator 45 can have a flat surface and/orrounded protrusions. Alternatively or additionally, the mechanicalactuator 45 can be larger or smaller than the size of the force sensor40. Optionally, the mechanical actuator 45 is about the same size as theforce sensor 40. The mechanical actuator 45 can be controlled to makecontact with a surface of the force sensor 40 and apply a force F3,which can be variable over time as described herein. Mechanical movementcan be controlled by means of one or more electrical motors, such as astepper or servo motor, for example. In some implementations, the systemoptionally includes a robotic arm, and the mechanical actuator 45 isoperably coupled to the robotic arm. For example, the mechanicalactuator 45 can be attached to the robotic end effector. The robotic armcan be configured to control the movements (e.g., trajectory, position,orientation, etc.) of the mechanical actuator 45 relative to the testfixture 44 such that a variable force can be applied by the mechanicalactuator 45 to the force sensor 40, as described above, mechanicalmovement can be controlled by means of one or more electrical motors.Robotic product testing systems are known in the art and are thereforenot described in further detail herein.

Additionally, the system includes the load cell 46. A load cell is atransducer that converts force into a measurable electrical output(e.g., a voltage). A strain gauge is one example type of load cell. Itshould be understood that other types of load cells can be used in thesystem described herein. Load cells are known in the art and aretherefore not described in further detail herein. The load cell 46 canbe arranged in series with the mechanical actuator 45. The force F3applied by the mechanical actuator 45 can be measured by a load cell 46.Optionally, the load cell 46 can be attached directly or indirectly tothe mechanical actuator 45. Optionally, the load cell 46 is not attachedto the mechanical actuator 45. It should be understood that thearrangement of the load cell 46 in FIG. 10 is provided only as anexample.

As described herein, applied force F3 in FIG. 10 can be variable overtime. For example, the mechanical actuator 45 can be controlled to applya first force (e.g., constant force F1 in FIG. 6) while simultaneouslyrecording the respective output signals from the force sensor 40 (e.g.,FIG. 7 prior to time t1′) and the load cell 46 (e.g., FIG. 6 prior totime t1). The mechanical actuator 45 can be further controlled tosubsequently ramp the first force to a second force (e.g., force F2 inFIG. 6) while simultaneously recording the respective output signalsfrom the force sensor 40 (e.g., FIG. 7 between times t1′ and t2′) andthe load cell 46 (e.g., FIG. 6 between times t1 and t2). The mechanicalactuator 45 can be further controlled to subsequently apply the secondforce (e.g., constant force F2 in FIG. 6) while simultaneously recordingthe respective output signals from the force sensor 40 (e.g., FIG. 7after to time t2′) and the load cell 46 (e.g., FIG. 6 after to time t2).Additionally, the transition from the first force to the ramped force(e.g., at time t1 in FIG. 6/t1′ in FIG. 7) and the transition from theramped force to the second force (e.g., at time t2 in FIG. 6/t2′ in FIG.7) serve as temporal data synchronization points between the respectiveoutput signals from the force sensor 40 and the load cell 46. Thesesynchronization points allow the force sensor output voltage to bedetermined as a function of load cell force measurement. Thisrelationship between force sensor output voltage and applied force isshown, for example, by FIG. 9.

It should be appreciated that the logical operations described hereinwith respect to the various figures may be implemented (1) as a sequenceof computer implemented acts or program modules (i.e., software) runningon a computing device (e.g., the computing device described in FIG. 11),(2) as interconnected machine logic circuits or circuit modules (i.e.,hardware) within the computing device and/or (3) a combination ofsoftware and hardware of the computing device. Thus, the logicaloperations discussed herein are not limited to any specific combinationof hardware and software. The implementation is a matter of choicedependent on the performance and other requirements of the computingdevice. Accordingly, the logical operations described herein arereferred to variously as operations, structural devices, acts, ormodules. These operations, structural devices, acts and modules may beimplemented in software, in firmware, in special purpose digital logic,and any combination thereof. It should also be appreciated that more orfewer operations may be performed than shown in the figures anddescribed herein. These operations may also be performed in a differentorder than those described herein.

Referring to FIG. 11, an example computing device 1100 upon which themethods described herein may be implemented is illustrated. Thecomputing device 1100 can be operably coupled to the mechanical actuatorand load cell described above, for example, and be configured to controlapplication of the force and record output data (e.g., output signals)from the load cell. Additionally, the computing device 1100 can beoperably coupled to the force sensor described above, for example, andbe configured to record output data (e.g., output signals) from theforce or strain sensor. It should be understood that the examplecomputing device 1100 is only one example of a suitable computingenvironment upon which the methods described herein may be implemented.Optionally, the computing device 1100 can be a well-known computingsystem including, but not limited to, personal computers, servers,handheld or laptop devices, multiprocessor systems, microprocessor-basedsystems, network personal computers (PCs), minicomputers, mainframecomputers, embedded systems, and/or distributed computing environmentsincluding a plurality of any of the above systems or devices.Distributed computing environments enable remote computing devices,which are connected to a communication network or other datatransmission medium, to perform various tasks. In the distributedcomputing environment, the program modules, applications, and other datamay be stored on local and/or remote computer storage media.

In its most basic configuration, computing device 1100 typicallyincludes at least one processing unit 1106 and system memory 1104.Depending on the exact configuration and type of computing device,system memory 1104 may be volatile (such as random access memory (RAM)),non-volatile (such as read-only memory (ROM), flash memory, etc.), orsome combination of the two. This most basic configuration isillustrated in FIG. 11 by dashed line 1102. The processing unit 1106 maybe a standard programmable processor that performs arithmetic and logicoperations necessary for operation of the computing device 1100. Thecomputing device 1100 may also include a bus or other communicationmechanism for communicating information among various components of thecomputing device 1100.

Computing device 1100 may have additional features/functionality. Forexample, computing device 1100 may include additional storage such asremovable storage 1108 and non-removable storage 1110 including, but notlimited to, magnetic or optical disks or tapes. Computing device 1100may also contain network connection(s) 1116 that allow the device tocommunicate with other devices. Computing device 1100 may also haveinput device(s) 1114 such as a keyboard, mouse, touch screen, etc.Output device(s) 1112 such as a display, speakers, printer, etc. mayalso be included. The additional devices may be connected to the bus inorder to facilitate communication of data among the components of thecomputing device 1100. All these devices are well known in the art andneed not be discussed at length here.

The processing unit 1106 may be configured to execute program codeencoded in tangible, computer-readable media. Tangible,computer-readable media refers to any media that is capable of providingdata that causes the computing device 1100 (i.e., a machine) to operatein a particular fashion. Various computer-readable media may be utilizedto provide instructions to the processing unit 1106 for execution.Example tangible, computer-readable media may include, but is notlimited to, volatile media, non-volatile media, removable media andnon-removable media implemented in any method or technology for storageof information such as computer readable instructions, data structures,program modules or other data. System memory 1104, removable storage1108, and non-removable storage 1110 are all examples of tangible,computer storage media. Example tangible, computer-readable recordingmedia include, but are not limited to, an integrated circuit (e.g.,field-programmable gate array or application-specific IC), a hard disk,an optical disk, a magneto-optical disk, a floppy disk, a magnetic tape,a holographic storage medium, a solid-state device, RAM, ROM,electrically erasable program read-only memory (EEPROM), flash memory orother memory technology, CD-ROM, digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices.

In an example implementation, the processing unit 1106 may executeprogram code stored in the system memory 1104. For example, the bus maycarry data to the system memory 1104, from which the processing unit1106 receives and executes instructions. The data received by the systemmemory 1104 may optionally be stored on the removable storage 1108 orthe non-removable storage 1110 before or after execution by theprocessing unit 1106.

It should be understood that the various techniques described herein maybe implemented in connection with hardware or software or, whereappropriate, with a combination thereof. Thus, the methods andapparatuses of the presently disclosed subject matter, or certainaspects or portions thereof, may take the form of program code (i.e.,instructions) embodied in tangible media, such as floppy diskettes,CD-ROMs, hard drives, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computing device, the machine becomes an apparatus forpracticing the presently disclosed subject matter. In the case ofprogram code execution on programmable computers, the computing devicegenerally includes a processor, a storage medium readable by theprocessor (including volatile and non-volatile memory and/or storageelements), at least one input device, and at least one output device.One or more programs may implement or utilize the processes described inconnection with the presently disclosed subject matter, e.g., throughthe use of an application programming interface (API), reusablecontrols, or the like. Such programs may be implemented in a high levelprocedural or object-oriented programming language to communicate with acomputer system. However, the program(s) can be implemented in assemblyor machine language, if desired. In any case, the language may be acompiled or interpreted language and it may be combined with hardwareimplementations.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A testing system, comprising: a test fixtureconfigured to provide electrical connection to a force or strain sensor;a mechanical actuator configured to apply a force to the force or strainsensor; a load cell configured to measure an amount of the force appliedto the force or strain sensor; and a controller configured to operatethe mechanical actuator and simultaneously record respective outputsignals from the force or strain sensor and the load cell.
 2. The systemof claim 1, wherein simultaneously recording respective output signalsfrom the force or strain sensor and the load cell comprises sampling therespective output signals in a burst mode, wherein the burst mode isdefined by a sampling frequency and a sampling period.
 3. The system ofclaim 2, wherein the respective output signal from the force or strainsensor is sampled with a first sampling frequency and a first samplingperiod.
 4. The system of claim 3, wherein the respective output signalfrom the load cell is sampled with a second sampling frequency and asecond sampling period.
 5. The system of claim 4, wherein the first andsecond sampling frequencies are the same.
 6. The system of claim 4,wherein the first and second sampling frequencies are different.
 7. Thesystem of any one of claims 1-6, wherein the force or strain sensorcomprises one or more piezoresistive, piezoelectric, or capacitivetransducers.
 8. The system of any one of claims 1-7, further comprisinga robotic arm, wherein the mechanical actuator is controlled by therobotic arm.
 9. The system of claim 8, wherein the robotic arm isoperably connected to and controlled by the controller.
 10. The systemof any one of claims 1-9, wherein the respective output signals recordedby the controller are stored in memory of the controller.
 11. The systemof any one of claims 1-10, wherein the respective output signals fromthe force or strain sensor and the load cell are recorded as a functionof time.
 12. The system of any one of claims 1-11, wherein thecontroller is configured to operate the mechanical actuator tocontinuously change the amount of the force applied by the mechanicalactuator from a first force value to a second force value, wherein thefirst and second force values are different.
 13. The system of claim 12,wherein the controller is further configured to: hold the first forcevalue constant while recording the respective output signals from theforce or strain sensor and the load cell as a function of time,subsequently ramp the first force value to the second force value whilerecording the respective output signals from the force or strain sensorand the load cell as a function of time, and hold the second force valueconstant while recording the respective output signals from the force orstrain sensor and the load cell as a function of time.
 14. The system of13, wherein the controller is further configured to use a transitionfrom the first force value to the ramped force and a transition from theramped force to the second force value as temporal data synchronizationpoints between the respective output signals from the force or strainsensor and the load cell.
 15. The system of any one of claims 1-14,further comprising a flexible substrate, wherein the force or strainsensor is soldered to the flexible substrate, and the force is appliedto the flexible substrate by the mechanical actuator to createdisplacement and strain within the flexible substrate and strain withinthe force or strain sensor.
 16. The system of claim 15, wherein therespective output signal of the force or strain sensor is recorded bythe controller through electrical routing within the flexible substrate.17. The system of any one of claims 1-16, wherein the system comprisesthe force or strain sensor.
 18. A method for testing a force or strainsensor, comprising: providing a test fixture configured to provideelectrical connection to the force or strain sensor; connecting theforce or strain sensor to the test fixture; operating a mechanicalactuator to apply a force to the force or strain sensor; providing aload cell configured to measure an amount of the force applied to theforce or strain sensor; and simultaneously recording respective outputsignals from the force or strain sensor and the load cell.
 19. Themethod of claim 18, wherein simultaneously recording respective outputsignals from the force or strain sensor and the load cell comprisessampling the respective output signals in a burst mode, wherein theburst mode is defined by a sampling frequency and a sampling period. 20.The method of claim 19, wherein the respective output signal from theforce or strain sensor is sampled with a first sampling frequency and afirst sampling period.
 21. The method of claim 20, wherein therespective output signal from the load cell is sampled with a secondsampling frequency and a second sampling period.
 22. The method of claim21, wherein the first and second sampling frequencies are the same. 23.The method of claim 21, wherein the first and second samplingfrequencies are different.
 24. The method of any one of claims 18-23,wherein the force or strain sensor detects strain throughpiezoresistive, piezoelectric, or capacitive transducers.
 25. The methodof any one of claims 18-24, wherein the mechanical actuator iscontrolled by a robotic arm.
 26. The method of claim 25, wherein therobotic arm is operably connected to and controlled by a computingdevice.
 27. The method of any one of claims 18-26, wherein therespective output signals from the force or strain sensor and the loadcell are stored in memory of a computing device.
 28. The method of anyone of claims 18-27, wherein the respective output signals from theforce or strain sensor and the load cell is recorded as a function oftime.
 29. The method of any one of claims 18-28, further comprisingcontinuously changing the amount of the force applied by the mechanicalactuator from a first force value to a second force value, wherein thefirst and second force values are different.
 30. The method of claim 29,further comprising: holding the first force value constant whilerecording the respective output signals from the force or strain sensorand the load cell as a function of time; subsequently ramping the firstforce value to the second force value while recording the respectiveoutput signals from the force or strain sensor and the load cell as afunction of time; and holding the second force value constant whilerecording the respective output signals from the force or strain sensorand the load cell as a function of time.
 31. The method of 30, furthercomprising using a transition from the first force value to the rampedforce and a transition from the ramped force to the second force valueas temporal data synchronization points between the respective outputsignals from the force or strain sensor and the load cell.
 32. Themethod of any one of claims 18-31, wherein the force or strain sensor issoldered to a flexible substrate, and the force is applied to theflexible substrate by the mechanical actuator to create displacement andstrain within the flexible substrate and strain within the force orstrain sensor.
 33. The method of claim 32, wherein the respective outputsignal of the force or strain sensor is recorded through electricalrouting within the flexible substrate.